H-1 magic angle spinning NMR gave firm evidence for formation of acidic protons (4.0 ppm) and hydride species (-1.8 ppm), where the former exists as OH groups (acidic protons) and the latter has an interaction with three equivalent Ag atoms, existing as Ag3H when Ag+-exchanged A-zeolite is reduced with hydrogen. The formations of Ag3H and of acidic protons by the heterolytic dissociation of H-2 over Ag-3(+) are reversible. The heterolytic dissociation of H-2 was also observed over Ag-Y-zeolite, the silver hydride species being observed at -0.1 ppm.